The front suspension system and supporting structures of a damaged vehicle must be checked to determine the real positions of the struts or other steering components with respect to the axle with a view to correcting any misalignment of struts or components that do not conform to specifications.
Three values must be examined in order to effect a correct alignment: the caster, the camber and the steering axis inclination. The caster is the angular relationship between the upper steering pivot and the lower steering pivot defined along the steering axis as viewed from the side of the vehicle; caster is measured in degrees from true vertical. The camber is the inward or outward tilt of the wheel as viewed from the front of the vehicle; camber is measured in degrees from true vertical. The steering axis inclination is the angle of an imaginary line through the upper steering pivot and the lower steering pivot of the steering axis as viewed from the front of the vehicle; this inclination is measured in degrees from true vertical.
Strut alignment gauges exist. For example, U.S. Pat. No. 4,453,315 issued June 12, 1984 to Mosiman et al, U.S. Pat. No. 4,498,242 issued Feb. 12, 1985 to Celette and U.S. Pat. No. 4,640,015 issued Feb. 3, 1987 to Mason all describe various types of gauges for measuring the displacement of automobile components with particular emphasis on the checking of the angular disposition of McPherson-type struts. The apparatus described in these patents allow the measurement of one or more of angles, such as camber, caster, toe-in and alignment. None, however, pertains to an apparatus which will measure the steering axis inclination and none enables the simultaneous measurements of caster, camber and steering axis inclination.